Lateral Effect Photodiode Research Articles

Quantum limits of position-sensitive photodiodes.

The split photodiode and the lateral effect photodiode are two popular detectors for measuring beam displacement. For small displacements of a Gaussian beam, which is the case of interest here, they are often seen as equivalent and used interchangeably, giving a signal proportional to the displacement. We show theoretically and experimentally that in the limit of low technical noise, where the signal to noise ratio is dominated by the shot noise of the light, the lateral effect photodiode produces a better signal to noise ratio than the split photodiode, owing to its optimum spatial detector response. This quantum advantage can be practically exploited in spite of the intrinsic thermal noise of the lateral effect photodiode.

A bias-free, lateral effect position sensor photo-detector

Lateral effect photodiodes sense the position of a laser beam by measuring the change of current between opposite anodes and a common cathode. They either require a bias current or the current is photogenerated. In either case, their linearity is affected by the non-uniformity of the current distribution between the anodes. We here propose a bias-free, lateral photo-diode, which consists of a resistive layer forming an extended Schottky contact to an intrinsic semiconductor. In our sensor, the photo-generated carriers do not diffuse laterally. Rather, their localization under the laser-beam results in a reduction of the barrier height due to image force effect. An open-circuit voltage appears between two opposite electrodes that is linear with the laser-beam position. A tetra-lateral configuration, with four anodes at the edges of a square-shaped sensor, allows sensing in two dimensions.

Design of an Angle Detector for Laser Beams Based on Grating Coupling

A novel angle detector for laser beams is designed in this paper. It takes advantage of grating coupling to couple the incident light into a slab waveguide; and, the incident light’s angle can be determined by reading the outputs of light detectors within the waveguide. This device offers fast-responding on-chip detection of laser beam’s angle. Compared to techniques based on quadrant photodiodes or lateral effect photodiodes, the device in this paper has far greater detectable range (up to a few degrees, to be specific). Performance of the laser angle detector in this paper is demonstrated by finite-difference-time-domain simulations. Numerical results show that, the detectable angle range can be adjusted by several design parameters and can reach [−4°, 4°]. The laser beam angle detector in this paper is expected to find various applications such as ultra-fast optical interconnects.

High-Speed Microscale Optical Tracking Using Digital Frequency-Domain Multiplexing

Position-sensitive detectors (PSDs), or lateral-effect photodiodes, are commonly used for high-speed, high-resolution optical position measurement. This paper describes the instrument design for multidimensional position and orientation measurement based on the simultaneous position measurement of multiple modulated sources using frequency-domain-multiplexed (FDM) PSDs. The important advantages of this optical configuration in comparison with laser/mirror combinations are that it has a large angular measurement range and allows the use of a probe that is small in comparison with the measurement volume. We review PSD characteristics and quantitative resolution limits, consider the lock-in amplifier measurement system as a communication link, discuss the application of FDM to PSDs, and make comparisons with time-domain techniques. We consider the phase-sensitive detector as a multirate DSP problem, explore parallels with Fourier spectral estimation and filter banks, discuss how to choose the modulation frequencies and sample rates that maximize channel isolation under design constraints, and describe efficient digital implementation. We also discuss hardware design considerations, sensor calibration, probe construction and calibration, and 3-D measurement by triangulation using two sensors. As an example, we characterize the resolution, speed, and accuracy of an instrument that measures the position and orientation of a 10 mm × 5 mm probe in 5 degrees of freedom (DOF) over a 30-mm cube with 4-μm peak-to-peak resolution at 1-kHz sampling.

Single Molecule Force Spectroscopy of Salt-dependent Bacteriophage T7 Gene 2.5 Protein Binding to Single-stranded DNA

The gene 2.5 protein (gp2.5) encoded by bacteriophage T7 binds preferentially to single-stranded DNA. This property is essential for its role in DNA replication and recombination in the phage-infected cell. gp2.5 lowers the phage lambda DNA melting force as measured by single molecule force spectroscopy. T7 gp2.5-Delta26C, lacking 26 acidic C-terminal residues, also reduces the melting force but at considerably lower concentrations. The equilibrium binding constants of these proteins to single-stranded DNA (ssDNA) as a function of salt concentration have been determined, and we found for example that gp2.5 binds with an affinity of (3.5 +/- 0.6) x 10(5) m(-1) in a 50 mm Na(+) solution, whereas the truncated protein binds to ssDNA with a much higher affinity of (7.8 +/- 0.9) x 10(7) m(-1) under the same solution conditions. T7 gp2.5-Delta26C binding to single-stranded DNA also exhibits a stronger salt dependence than the full-length protein. The data are consistent with a model in which a dimeric gp2.5 must dissociate prior to binding to ssDNA, a dissociation that consists of a weak non-electrostatic and a strong electrostatic component.

Development of the Lateral Effect Photo Diode Technique to Measure Oil Film Thickness

A measurement technique was developed using the lateral effect photodiode method to determine oil film thickness and oil retention measurement. A position-sensing photodiode determined the change in position of a focused laser beam. The beam was reflected off a diffuse body and calibrated to varying surface deflections. The calibration showed accuracy to 1 um. Samples of tool steel were prepared with a specific surface topography and then applied with a predetermined amount of heavy white mineral oil. The resulting film of the mineral oil was then observed, measured and recorded using the lateral effect photo diode method. Experiments were also run with a pin-on-disk machine to measure the oil film thickness produced at varying sliding speeds. The experiments showed that the lateral effect photo diode technique can measure oil films in a lab environment. Presented at the 51st Annual Meeting In Cincinnati, Ohio May 19–23, 1996

Measurements of a fabricated micro mirror using a lateral-effect position-sensitive photodiode

The characteristics of a fabricated micro mirror were determined using an optical measurement system. The system consisted of a helium-neon laser, a p-i-n lateral-effect photodiode, and other fundamental optical elements. For testing, we used a micro mirror array (1/spl times/4) in which each mirror was composed of a mirror plate, two torsional flexure hinges, two address electrodes, and two support posts. A mirror plate was designed to a size of 100/spl times/110/spl times/1.5 /spl mu/m/sup 3/ and the hinge size was 20 /spl mu/m long, 5 /spl mu/m wide, and 0.5 /spl mu/m thick. The micro mirror array was fabricated using micromachining technology and a lithography-galvanoformung-abformung-like process using nickel electroplating. The variation in the mirror's deflection angle with applied voltage was measured as a static characteristic. The downward threshold voltage of the 0.5-/spl mu/m thick hinge was 48 V. The step response time, as a dynamic characteristic, was 21.8 /spl mu/s when a 64 V step voltage higher than the downward threshold voltage was applied to an address electrode. The lifetime of the fabricated micro mirror was tested for both unidirectional and bidirectional operation.

Displacement sensing resolution of position-sensitive detectors in atmospheric turbulence using retroreflected beam

The position sensing resolution of a lateral-effect photodiode (LEP) and a four-quadrant (4Q) photodetector used as the position sensitive detector (PSD) in a sensor which measures the lateral displacement of a corner cube reflector (CCR) by illuminating it and detecting the position of the reflected light spot with the PSD is studied. An LEP is much noisier than a 4Q detector, but in an outdoor environment the sensitivity of the 4Q detector to atmospheric turbulence due to defocusing makes its resolution worse than that of an LEP. Submillimeter resolutions at the target distances of several hundreds of meters are electrically achievable with an LEP. Outdoors, however, its resolution is also bounded by the atmospheric turbulence. In turbulent measurement conditions, standard deviations of better than 1 cm were typically achievable up to the distance of 300 m and about 10 cm up to half a kilometer.

An intelligent active range sensor for mobile robot guidance

The mechatronic design of an eye-safe laser rangefinder, based on the lateral-effect photodiode (LEP) and synchronised scanning, is described. The sensor acquires two-dimensional range data, which has been found sufficient to guide the local manoeuvres of a mobile robot in most environments. An analysis of LEP operation shows that image position measurement repeatability, normalised with respect to the detector half length, is equal to the signal current to noise current ratio. This result suggests a method for estimating the noise density of the measurement process and, along with a geometric model of the ranging process, allows accurate estimation of the variance of individual range measurements, making the sensor particularly amenable to statistically based range feature detection, tracking, and data fusion algorithms. The sensor is active, in the sense that it can change the orientation of its field of view, in order to track useful and stable range features. Range data acquisition, range feature extraction, and control of the active head behaviour are all implemented on a local network of six transputers. This parallel structure is described and it is shown how the sensor constitutes an intelligent agent in a balanced sensor suite for the guidance of close range mobile robot manoeuvres.

CMOS photodetectors for industrial position sensing

The properties of a CMOS-compatible pn-photodiode, phototransistor, and one-dimensional lateral-effect photodiode (LEP) for position-sensing applications are characterized. The photodiode and phototransistor seem to have properties that are comparable to typical commercial photodetectors despite the relatively large variations in their spatial and spectral responses and the lower responsivity in the near-infrared band. In addition to the above properties the LEP's show excellent linearity, but 3-4 times larger NEP than corresponding commercial LEP's due to low resistance of the current dividing layer. The responsivity variations have no effect on the linearity of the LEP, and the slightly lower responsivity at near-infrared has only a negligible effect on the achievable resolution (SNR). These properties, usually considered as weak points of CMOS-compatible photodetectors, are believed to have little or no effect on the properties of a position sensor, if the diameter of the light spot is small (<100 /spl mu/m). CMOS-compatible photodetectors are therefore believed to be very suitable for industrial position-sensing applications.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A Lateral-Effect Photodiode Scanning Sensor for Autonomous Vehicle Manoeuvres

A large field of view laser scanning sensor, based on the lateral-effect photodiode, and designed for close range mobile robot manoeuvres, is described. Laser modulation and synchronous detection are used to approach the theoretical white noise limit of sensor performance. Noise in the system, which determines ranging accuracy, is determined from logarithmic plots of signal strength and image resolution against range. The results suggest that sensor accuracy is around 82% above the theoretical performance limit. Finally, some typical scans are presented

Real-time positioning of moving objects by dynamic target tracking

Positioning and navigation of construction machines are one aim in the Special Research Center on “High Precision Navigation”, an interdisciplinary project at the university of Stuttgart (FRG). The positioning is done by a system of several electronic cameras containing lateral effect photodiodes in the image planes. Two modes of measurement are described: With a minimum of two fixed cameras the positioning is possible in a limited working space. The elimination of reflections along with system calibration leads to a high accuracy in object space of at least 1 : 10000. As an example the dynamic survey of an industrial robot is presented. With electronic cameras mounted on a motorized theodolite the system works as a highly precise dynamci surveying robot for guidance of machines on construction sites. This system is a powerful dynamic measurement tool in competition with CCD-cameras-based systems and works already with small desktop computers.

Alignment of a three-mirror off-axis telescope by reverse optimization

A three-mirror off-axis telescope was aligned by ray aberration measurement and reverse optimization, which is the technique of creating a computer model of the telescope in its misaligned state. A set of Hartmann measurements were made at multiple field points and multiple focus planes. The Hartmann data were then used as targets for the ACCOS V lens design code that created via least squares optimization a misaligned model of the telescope to match the measurements. The physical telescope components were then moved opposite the misalignments of the model. The Hartmann pattern was generated using a five-hole Hartmann screen and measured by the use of a position-sensing, lateral-effect photodiode. Our results show this method is a viable tool for assisting in the alignment of optical systems.

A real-time optical 3D tracker for head-mounted display systems

In this paper, a new optical system for real-time, three-dimensional position tracking is described. This system adopts an "inside-out" tracking paradigm. The working environment is a room where the ceiling is lined with a regular pattern of infrared LEDs flashing under the system's control. Three cameras are mounted on a helmet which the user wears. Each camera uses a lateral effect photodiode as the recording surface. The 2D positions of the LED images inside the field of view of the cameras are detected and reported in real time. The measured 2D image positions and the known 3D positions of the LEDs are used to compute the position and orientation of the camera assembly in space.We have designed an iterative algorithm to estimate the 3D position of the camera assembly in space. The algorithm is a generalized version of the Church's method, and allows for multiple cameras with nonconvergent nodal points. Several equations are formulated to predict the system's error analytically. The requirements of accuracy, speed, adequate working volume, light weight and small size of the tracker are also addressed.A prototype was designed and built to demonstrate the integration and coordination of all essential components of the new tracker. This prototype uses off-the-shelf components and can be easily duplicated. Our results indicate that the new system significantly out-performs other existing systems. The new tracker provides more than 200 updates per second, registers 0.1-degree rotational movements and 2-millimeter translational movements, and processes a working volume about 1,000 ft 3 (10 ft on each side).

Design of Bessel-type transimpedance preamplifiers for lateral-effect photodiodes

A series of design guidelines is introduced for Bessel-type (maximally flat delay) transimpedance preamplifiers for optimum position detection using a lateral-effect photodiode. A distributed parameter network model for the lateral-effect photo-diode and a one-pole model for the preamplifiers are used in a complete analysis of the sensor. The analysis yields the necessary unity gain bandwidth of the preamplifiers for a given transimpedance gain and positioning resistance and junction capacitance of the detector such that constant group delay is achieved within the prescribed bandwidth. This criterion ensures that the position of edges is not affected by the response of the preamplifiers. Experimental results are provided to demonstrate the technique for video and quasi-video bandwidths. The analysis is complemented by the derivation of equations for the temperature drift and the noise level of the combined lateral-effect photo-diode and preamplifiers. These equations clearly show the presence of crosstalk...

Testing optics by experimental ray tracing with a lateral effect photodiode

We demonstrate a method for testing optics (spherical and aspheric) and other reflecting or transmitting objects. We call this experimental ray tracing. A laser beam is sent through the sample, and its propagation is determined with a lateral effect photodiode. A modified Hartmann test can be performed by measurement of beam location within two planes. Measurement in one plane close to the focus delivers a spot diagram. The method is well suited for testing even strong aspheric optics. As a further use we demonstrate 3-D shape measurement of nonplanar glass plates, e.g., car windshields.

A precision laser-trigonometer.

This paper reviews a laser-trigonometer which utilizes laser diode as a light source and lateral-effect photodiode as a position-sensing device. The principle of operation and signal processing in the instrument are described. Several application areas are outlined.

Measuring workpiece dimensions using a non-contact laser detector system

Proper process control procedures are important considerations in the optimisation of any manufacturing process. Ultimately, a continuous update on the size and quality of the products being manufactured is desirable. A non-contact laser detector system was developed to measure the dimensions of wood products in a real-time operating environment, employing a two-axis lateral effect photodiode as the sensor. Computer algorithms were developed to measure the thickness, warp, and width of wood samples (pencil slats). The effect of mechanical vibration due to slat transport was identified and when possible eliminated. The system was evaluated at different transport speeds. The results indicated that, except for width measurement which is limited by the computing speed, the system can measure thickness and warp quite accurately at feed speeds of 240 feet per minute. Although the work described is specific to certain applications, the implications for use in other industrial activities where visual sensing is required is apparent.

High-precision, wide-range, dual-axis, angle monitoring system

A system is described that uses a helium–neon laser and lateral effect photodiodes to monitor the θ and φ angles of a test mirror. Accuracies of 0.01 arcsec are achieved short term in a laboratory environment. A bandwidth of 900 Hz allows simultaneous real-time angle monitoring on both coarse (10 000 arcsec) and fine (300 arcsec) angular ranges.

Lateral effect photodiode: a new technique to obtain position signals

Lateral effect photodiode: a new technique to obtain position signals